For many, Destiny is something of an enigma. There has been grand talk about how this $500m video game, developed by the studio that made Microsoft’s flagship console series Halo, will reinvent the first-person shooter, a monolithic and lucrative genre that stands front and centre of the medium. But the nature of that reinvention has remained, despite numerous press trips to developer Bungie’s studios in Seattle, somewhat opaque.

Now, finally, Destiny is playable – at least for the lucky few to be selected for its public Alpha. Once experienced, Destiny’s sell is more straightforward: this is a shooter married with a massively multiplayer online (MMO) adventure, a blend of Activision’s two greatest and most financially successful game series: Call of Duty and World of Warcraft.

As in any MMO, you begin by choosing your character’s class (at this time one of three options, although logically more will follow). There’s the Titan (the character that looks and plays closest to Halo’s protagonist space marine, Master Chief), the Hunter (the class that combines weapons proficiency with space magic) and the Warlock, the mage of the group. Each class has its own weapons, skills and list of expanding abilities that are unlocked when, as in World of Warcraft, your avatar level's up. This is achieved by earning experience points through completing missions.

'Destiny is simply our next shooter'

Pete Parsons, Bungie’s COO prefers to distance the game from these obvious reference points. “Destiny is simply our next shooter,” he told me during an interview at this year’s E3 video game conference in Los Angeles, the day before the Alpha launched. “I had the great fortune to be with Bungie when we made the first Halo and, as funny as it might seem today, it was incredibly difficult to explain that game before it was launched too. But for us, this is the logical leap forward. I’m not trying to reinvent the name: it’s simply our next shooter, the game that we’ve wanted to make for a long time.”

Nevertheless, Destiny invites strong comparisons to well-established MMOs, at least in terms of its structure if not its setting and feel. Missions are played out on Earth, and specifically (at least, in the Alpha) a far future Russia, where the only artifacts of Soviet power are the tank turrets poking from the verdant overgrowth. New tasks are doled out from blinking beacons in the landscape – kill a set number of these enemies, collect a set number of those items – and the satisfying compulsion loops of the role-playing game are immediately obvious.

The game feels like a Halo title, however, and that’s what marks Destiny out from the crowd. Characters enjoy Master Chief’s lingering leaps (a double jump allows each character to hover in the air for a few seconds), a limited number of switchable weapons and similar thirty second loops of intense combat play.

Destiny at E3 2014

Destiny’s impressive, if largely hidden technological miracle, is the way in which it joins up your game with those of other players on the server, without the use of any menu screens. Rather, people are matched dynamically, able to work together in Strike teams to complete objectives, or simply go about their solitary business within the same area. Occasionally, a dynamic public multiplayer mission will pop-up while you’re in the middle of another task, a giant tank that requires four or five players to take it down, for example. But again, you don't have to engage; this is a universe that supports solitary adventurers as well as social combatants.

All players earn loot from completing missions – and occasionally you’ll find treasure chests laying about. New guns, pieces of armour and so on can be used to customise your character’s appearance and to make him or her more effective on the battlefield.

Some enemies drop schematics that let you forge new weapons and armour. When you tire of fighting on Earth you can exit to the safety of your spaceship which waits patiently in orbit (this too can be customised in appearance to your liking) and visit one of the game’s other areas: a player vs. player arena, where competition, not co-operation is encouraged, or the Tower, a kind of space sanctuary where you meet up with other players and buy new items using Glimmer, Destiny’s in-game currency.

The lure of microtransactions

While Bungie has been unequivocal that Destiny will not be a subscription service like its cousin World of Warcraft, the game seems well-suited to microtransactions post-launch. Glimmer is shared between all of your characters (the game encourages you to have more than one to your name) and it’s only a short leap to imagine Bungie will sell currency packs with which players will be able to purchase powerful weapons or striking armour – particularly if there is no accompanying subscription to fund the game’s on-going development.

“I think we were one of the first people to offer DLC with Halo 2 and players responded extremely well to that,” says Parsons, who won’t be drawn on the subject. “We want to keep expanding the world, but in the best way. I won’t go into the details of how that will happen but I think we’ll do it in a way that people feel excited by and supportive of.”

What is clear is that, while we are now clearer on Destiny’s nature, there are many surprises left to come.

•Destiny is released on PS3, PS4, Xbox 360 and Xbox One on 9 September

One of the biggest new games of the decade goes on sale this week but what exactly is a “shared-world shooter”? Here is a quick guide for those whose children, partners or parents are about to disappear into space. By Keith Stuart